Drilling muds



United States Patent DRILLING MUDS Rodolfo J. Tailleur, San Tome, Venezuela, assignor to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application October 28, 1954,

Serial No. 465,418

21 Claims. (Cl. 252-85) This invention relates to improvements in drilling mud compositions of the type used in well drilling, and more particularly it pertains to oil-in-water emulsion drilling muds having improved lubricating properties.

A substantial portion of the total time consumed during well drilling operations is taken up in the replacement of drill bits. Inasmuch as changing a bit necessi tates pulling the entire string of drill stern, substituting a new bit, and rerunning the entire string of drill stern back into the borehole, it is evident that the time consumed in making bit changes increases roughly in proportion to the depth being drilled. As wells are being drilled to ever increasing depths, the economic losses attendant upon the increasing amount of time lost in making bit changes cannot be ignored. In addition to the loss of time involved inmaking bit changes, the necessity for making frequent bit changes, particularly when drilling at substantial depths, may create hazards, such as increasing the likelihood of cave-ins, which may arise as a result of stopping the circulation of the drilling mud during the change of bits.

Obviously, the necessity for making a bit change 18 dictated by the exhaustion of the useful life of the bit. Although much has been done toward improving drill bits and drilling techniques in order to prolong useful life, in the present state of rotary bit development, the mostfrequent limiting factor of bit life is failure of the bearings, rather than the cutting teeth.

Thus, perhaps the most important factor tending to shorten the useful life of a drill bit is the lack of adequate lubrication of the bearings. In the past, efforts have been made to afford lubrication for the bearings by incorporating self-contained lubricating units in the bits. That such efliorts have not been entirely successful is borne out by the fact that conventional bits currently in use are not provided with such self-lubricating units. Consequently, conventional bits receive only such lubrication as may be obtained from the drilling mud being circulated therethrough. Since the bearings of the bit are subjected to high loads, the value of conventional drilling muds as bit lubricants leaves much to be desired.

Although lubricating properties have commonly been attributed to conventional oil-in-Water emulsion drilling muds, as far as I am aware, it has not been satisfactorily demonstrated that such muds actually behave as lubricants for the bearings of drill bits under actual field conditions which impose high specific loads on the bearings of the bit. I have investigated some commonly used oil-- in-water emulsion drilling muds to which lubricating properties have been attributed, and on the basis of field tests and tests made with the Timken wear and lubricant tester, I have found that the lubricating properties of such muds are of no significance with respect to the specific loads on the bearings under the conditions to which a drill bit is subjected in the field. In other Words, under such conditions, such muds have practically no lubricating value for the bearings of drill bits. i

I have now discovered that oil-in-water emulsion drill- I tent of about 5.2 percent.

ing muds can be made to possess efiective lubricating properties and thus prolong the life of drill bits while retaining the normally desirable properties of such muds. In accordance with my invention, I provide a drilling mud which is an emulsion of oil-in-water containing clay solids, and an asphalt in the oil phase, said asphalt having chemically combined sulfur and being present in an amount sufficient to provide at least about one percent of sulfur by weight of the oil phase. Such drilling muds possess excellent lubricating qualities and prolong the life of the bearings of drill bits, thereby reducing the frequency of bit changes and decreasing the time diverted from actual drilling operations.

The asphalts utilized in the muds of my invention inelude such materials as natural asphalts, petroleum asphalts, reduced crudes, blown asphalts, the solid petroleum residues or pitches obtained in the vacuum reduction of crude oils and such asphaltites as manjak or glance pitch and grahamite, provided that the foregoing materials contain such an amount of sulfur that upon incorporation into the oil phase of the drilling muds they provide at least about one percent of sulfur by weight of the oil phase.

It will be understood by those skilled in the art that the sulfur content of various asphalts will vary, depending on their source and/ or the specific methods by which they have been prepared. For example, crude asphaltic PEII'O'. leum oils high in sulfur may yield asphalts of a relatively high sulfur content if the sulfur tends to concentrate in the residual fractions during distillation. Similarly, the depth of reduction of an asphaltic crude oil can determine the sulfur content of the asphalt residues obtained. Among the natural asphalts, the sulfur content appears to depend primarily on the source of the asphalt, although in the case of the asphaltites the type of asphaltite is important, manjak and grahamite containing sutficient amounts of sulfur whereas gilsonite does not. In general, in order to provide the desired sulfur content in the oil phase, and having regard for the asphalt concentration in the oil phase as will be elaborated below, the asphaltic materials employed in the oil phase must contain at least about 1.5 percent of sulfur by weight. As is known in the art, the sulfur in such asphaltic materials is chemically combined in the form of sulfur-hydrocarbon complexes of high molecular weight.

The asphalts themselves are well-known materials, the properties and preparation of which have been detailed in the art. They range from highly viscous liquids to semi-solid to essentially solid materials. Since the as phalts in the muds of my invention are part of the oil phase, it is desirable that they dissolve or disperse readily to become uniformly blended in the oil employed in the oil phase. The preferred asphaltie materials are therefore those of a relatively high sulfur content, possessing the property of ready solubility or dispersibility in the distillate petroleum fractions commonly employed in the oil phase of oil-in-water emulsion drilling muds. For example, one preferred asphaltic material is a reduced Kuwait crude from the Burgan field, having a flash point of about 650 F. or somewhat higher and a sulfur con- This material is readily dispersed in a gas oil of the diesel fuel type without any diificulty, for example, in proportions of reduced crude todiesel fuel ranging from 1:1 to 3:1 by volume. Similarly, there exist other asphalt-containing petroleum residues of a relatively high sulfur content, for example, residues obtained from Eastern and Western Venezuelan crudes, Iranian crudes and West Texas crudes, which can be cutback or thinned with a petroleum distillate fraction, such as a light or heavy catalytically cracked cycle oil 111 the gas oil boiling range, and these constitute preferred materials.

asphalt-containing oil phase by employing as the oil phase in the muds of my invention a residual fuel oil of the type of No. 6 fuel oil, such oils being available with sulfur contents of from about 2 to 3.5 percent. Similarly, topped or reduced crudes containing sulficient sulfur can be cut back or thinned with suitable petroleum solvents to form the entire oil phase. In some instances, depending upon the nature of the crude oil, it is "possible to employ the entire residue from a topping operation as the oil phase, such topping residues containing sufiicient asphaltic material of the desired sulfur content and sufficient oil to make up the remainder of the oil phase.

In the event more ditficultly soluble asphaltic materials are employed, it is desirable to employ in the oil phase oils of higher solvency such as highly aromatic petroleum distillates or the liquid extracts obtained in the solvent refining of. lubricating oils. Additionally or alternatively, an auxiliary solvent or blending agent, for

example; liquid chlorinated diphenyl or the above-mentio ned liquid solvent extracts 'can be employed to obtain the desired uniform blend of the asphalt in the oil phase. Incorporation of the asphalts in the oil phase can also be facilitated by initially melting or finely dividing the material prior to adding the 'oil, and/or h asphalt mixture to about 1.80 F.

The amount of sulfur-containing asphalt employed in the oil phase to provide at. least about one percent of sulfur by weight of the oil phase will vary with the sulfur content of the particular asphaltic material employed. For example, withan asphaltic material such as'a manjak containing about 10 percent by Weight of sulfur, at least 10 percent of the manjak must be employed to obtain a sulfur content of at least one percent of the oil phase. With asphaltic materials containing less sulfur, larger amounts of asphalt must be employed. As a practical maximum, it is undesirable to employ more than about 75 percent by'weight of asphalt in the oil phase because there are then obtained unstable emulsions which tend to foam excessively. Furthermore, the viscosity of the oil phase containing such large amounts of asphalt is so high as to approach the solid state, causing difiiculties in handling at the well site. Accordingly, the asphalt should contain not less than about 1.5 percent of sulfur to provide the necessary sulfur content in the oil phase without encountering the above-mentioned difficulties.

Since the oil phase of my oil-in-water emulsion drilling muds contains substantial amounts of asphaltic materials, as has been shown hereinabove, the oil employed in the oil phase is a non-residual o-r distillate oil, such as gas oils, kerosenes, diesel fuel oils, distillate lubricating oils, the liquid extract fractions obtained in the solvent refining of lubricating oils, or mixtures of such oils. It has already been pointed out in connection with the description of the sulfur-containing asphalts that certain 'of the latter materials canbe obtained in solution in petroleum'distillates In such instances, the further addition of a distillate oil to such asphalt-containing materials is ordinarily unnecessary, particular reference being made to the asphalt cutbacks, residual fuel oils and the'topped crudes containing sufiicient distillate fractions, as already described, which constitute the entire oil phase. The total oil phase of the drilling muds of the invention ranges from about 2 to 40 percent by volume of the entire drilling mud, preferably from about 5 to percent. The emulsifying agent, presently to be described, isalso considered to be part of the oil phase for the purpose of determining the amount of total oil phase in the mud.

Since the drilling muds of my invention are oil-inwater emulsion drilling muds, an emulsifying agent will normally be added during preparation of the muds to facilitate emulsification or dispersion of the oil phase in the water phase and to stabilize the emulsion obtained.

eating the oil- Numerous emulsifying agents for preparing oil-in-water .emulsions are known inthe art and any of-such conventional emulsifying agents can be employed for the above purposes.

However, in the use under drilling conditions of oilin-water emulsion drilling muds, it is desirable that the mud filtrate have a low surface tension, say on the order of 40 dynes per centimeter or below. Since emulsifying agents are surface-active compounds, they will also act to reduce the surface tension of the filtrate; although not all emulsifying agents are of equal effect for this purpo e. In a preferred embodiment of thy invention, my drilling muds therefore contain an emulsifying agent which not onlyserves to assist in the eniu'lsiflcation of the oil and to stabilize the emulsions formed, but substantially to feduce the surface tension of the filtrate as well, I have found that emulsifying agents which are particularly suitable for the latter purpose include preferentially oil-soluble alkylaryl sulfonic acids, e. g., wax benzene sulfonic acids and mahogany acids, and metal salts thereof, e. g., the alkali metal, ammonium and alkaline earth metal, including calcium and magnesium, salts. sodium soaps of tall oil and the fatty acid esters of the anhydroalkitols, for example, sorbitan, mono-, di-, or tri-oleate, sorbitan mono-stearate, etc. Of the above emulsifying agents, I prefer to employ the sodium salt of mahogany acids, because not only is it more effective in achieving the desired reduction in surface tension of the filtrate, but it can be used in smaller amounts for this purpose than other emulsifying agents. Substantial economies can therefore be achieved.

In general, satisfactory results with respect to reducing the surface tension of the filtrate and stabilizing the emulsion can be obtained by the use of from about 1 to 4 pounds of emulsifying agent per barrel of the entire drilling mud composition, sufficient to reduce the surface tension of the filtrate substantially below that of water and preferably to about 40 dynes per centimeter or less. However, when using the preferred emulsifying agent, namely, the sodium'salt of mahogany acids, it is highly advantageous to employ not more than about 2 pounds per barrel in order to avoid excessive oil loss in the filtrate, as fully set forth in my copending application;

Serial No. 350,460, filed April 22, 1953, now U'. S. Patent No. 2,713,032. v

Any clay can be utilized in the drilling muds of this invention which is commonly employed for this purpose in the art. Such clays, which form dispersions or gels with water, can be native products, such as may be available at the well site, or a relatively pure clay, such as bentonite, or base-exchanged clays, such as lime-treated clays, etc. In general, when using clays such as benf: tonite, the clay is employed in an amount of from about 2 to 8 percent by weight of the entire compositiomm'ore or less, depending upon the yield (barrels of mud of 1 55 centipoise viscosity per ton of clay) of the clay. When native clays are employed, larger amounts, say as hi'gHas 40 percent by weight of the mud composition, ca beu's'cd because they yield less barrels of mud per ton of clay.

'-'It' is characteristic of the drilling muds of this invention that they are sensitive to the presence of alkali metal hydroxides. By this I mean that the addition of substan tial quantities of alkali metal hydroxide to these; muds results in a loss of the lubricating properties otherwise obtained through the use of the sulfur-containing asphaltic material in the oil phase.

'Similarly,'a drilling mud which has already been treated with substantial amounts of alkali metal hydroxide does not respond beneficially to later treatment with the sulfur-I containing asphalt. In other words, notwithstandingthe fact that oil-in-water emulsion drilling muds contain a sulfur-containing asphalt, such muds will not have enhanced lubricating properties in the presence of alkali metal hydroxide. Thisphenomenon is unexpectedl anii' Other suitable emulsifying agents include the.

cannot be satisfactorily'explained at present, particularly since the lubricating properties of the muds of this inven-- tion are not detrimentally affected by admixture with such materials as calcium hydroxide or sodium chloride.

The sensitivity of the drilling muds to alkali metal hydroxide imposes certain precautions in the use of clay defiocculants to reduce the viscosity and fluid loss of the muds. For example, one of the most widely used clay defiocculants is quebracho which is generally employed with caustic soda. If the drilling muds of this invention are treated in the usual manner with the conventional quebracho-caustic soda mixture, there results a loss of. the enhanced lubricating properties, although the otherwise normal properties of the muds are retained. It is to be noted, however, that the muds of the invention will tolerate a limited amount of caustic soda without losing their load-carrying capacities. The limits ofsuch tolerance are diflicult to specify exactly since they will vary with the nature and amount of the clay in the drilling mud. For example, with a drilling mud made in accordance with this invention, containing pure bentonite as the clay in an amount of 6 percent by weight of the entire mud and having a relatively high tolerance to alkali metal hydroxides, I have found that the use of 0.5 pound of caustic soda per barrel of drilling mud, although reducing the load-carrying capacity considerably, does not render the mud Worthless from a lubricating standpoint. However, when the caustic soda is increased to 1.0 pound per barrel of the mud, the lubricating properties of the mud are substantially eliminated. With other clays, the caustic soda tolerance is substantially less.

From the foregoing, it will be apparent to those skilled in the art that no substantial amount of caustic sodashould be added to the muds of this invention; in no event should such amount be suflicient to destroy the enhanced lubricating properties of the muds. Since in normal field practice, the amounts of caustic sodausually employed, particularly in connection with quebracho treatment, are in substantial excess of the amounts deleteriously affecting the lubricating properties of the muds of the invention, when it becomes desirable to use an alkaline treating agent with or without a clay dejoint use of caustic soda, although in such case more of I the quebracho will usually be required to obtain the desired deflocculating efiect.

In theactual practice of my invention, it is permissible to conduct the entire drilling operation with the drilling muds above described. However, initial drillingoperations can be started with a conventional straight.

water-base mud because the soft formations and the ab sence of high specific loads on the drill bit at the shale...

lower depths do not require greater lubricating properties than can be obtained with a water-base mud. Thereif after, as dictated by the requirements of drilling and the formations encountered, the water-base mud is con- H verted to the mud of my invention. can readily be accomplished during circulation of the water-base drilling mud in the well by adding to the mud in the mud pit a sulfur-containing asphalt and an oil, either separately or in admixture in the form of a cutback, and an emulsifying agent. These materials are added in anamount dependent upon the total amount of the drilling mud already in the system and preferably at a rate dependent upon the rate of drilling mud cir culation, so as to effect a substantially uniform dispersion of the oily materials as an oil phase throughout the drilling mudsystem. Conventional methods can be employed forwhatever mechanical agitation is necessary to achieve the proper mixing. It is highly desirable :to. ad d the This conversion emulsifying agent to the water-base drilling mudin .admixture with the oil,- but if added separately, it isad visablethat it be added after the oil has been added or simultaneously with the addition of the oil. If the emulsifying agent is added prior to addition of the oil phase, there is a tendency for the mud to foam excessively and this entails the risk of a blowout.

In the practice of my invention, it is also possible to convert an existing conventional oil-in-water emulsion drilling mud to a drilling mud in accordance with my invention. This is also accomplished during circulation of the drilling mud in the well by adding thereto, with agitation with the drilling mud in the usual mud pit, a sulfur-containing asphalt or a concentrate-thereof in oil.' The concentrate can also contain an emulsifying agent. The total amount of sulfur-containing asphalt or the oil concentrate thereof and the concentration of the components therein are such that the concentrationof the components of the resulting drilling mud composi tion being prepared,taking into account the composition of the conventional oil-in-water emulsion drilling mud being converted,.will result in an oil-in-water emulsion drilling mud having the composition of the muds of my invention, as set forth in detail above.

It will be understood that the drilling muds of my invention which have become depleted in one or more components during use can be treated with the depleted components or oil concentratesthereof to restore the desired concentration of such components.

As an example of the preparation and use of one of the preferred embodiments of my invention in drilling a well, about the first two thousand feet of hole are drilled using as the drilling mud the mud formed from water and the natural clays'incorporated therein from the formations during'the drilling. In case such formations are deficient in natural clays, it is permissible to add a small quantity of bentonite to the drilling mud to increase the viscosity and thixotropic and wall building properties thereof. Up to this point, the procedure is identical with normal drilling operations where straight water-base drilling muds are employed. At this stage,

the water-base drilling mud in the system totals about- 500 barrels (barrel throughout the specification and claims is 42 standard U. S. gallons). It having been determined that conversion to an oil-in-water emulsion drilling mud is now desirable, an oil phase is prepared as follows. Into a suitable mixing vessel, there are placed 11.5 barrels of a diesel fuel oil, 34.5 barrels of a reduced Kuwait crude from the Burgan field, having an API gravity of 5.9, a flash point of 665 F. and a sulfur content of about 5.2 percent, and 4 barrels of an oil concentrate of the sodium salts of mahogany acids (the con-' c'entrate being available commercially as Petronate HL,-

containing percent by weight of thejsalts dissolved in a lubricating oil). The mixture is stirred until all of the-'- components are uniformly blended. The oily composil tion thus prepared, which is to constitute the oil phase-- of the drilling mud, amounts to about 50 barrels and.

is a moderately viscous, black liquid that can be pumped readily at ordinary temperatures andemulsifies readily.

in the mud to form an oil-in-water emulsion. The oily f composition is then added to the straight water-base drill-. ing mud by circulating the mud through the well while pouring the oily composition into the mud ditch through which drilling mud returns to the mud pits from the well and agitating the pits with mud guns. Drilling need notbe discontinued during the change from a water-base mud to the oil-in-water emulsion mud of my invention. 'Aftei' all of the oily composition has been added to the preexisting drilling mud and after the mixture has been circulated through the well about two or three times, the entire drilling mud in the system is a uniform oil-in heretofore .described.

7 In: the following. illustrative examples, there are set forth ce'rtain specific embodiments of the drilling mud compositions ot the invention. It will be understood that these specific embodiments are given by way'of'il- 8 1.00 grams afiter seconds. The martial: had a sulfur content of 9 1 percent. by weight. The reduced. Kuwait crude had an API gravity of 5.9, a flash point of 665 F. andasulfur content of about 5.2 percent.

lustrationonly and are-not intended to limit the invention. 5 Under the heading Oil in the table, the Naphthenic It will be noted that, in determining the improvement Extract 'No. 1 was the oily material'obtained as the in lubricating properties of the drilling muds, I have extract fraction; in the solvent extraction of a 400 Texas employed the well-known Timken wear and lubricant lubricating distillate with furfural. The extract had: an tester. This machine is employed in: thelubricating' oil API' gravity of 145 and a viscosity of 1170: S118. at art to determine the load-carryingv capacity of lubricants. 10' 100 F. The Diesel Fuel Oil employed had a gravity Itwas obviously impractical to test the lubricating properof about 35 API, a. flash point of about 178 F. and a ties of all the drilling muds set forth in each of the boiling range ofabout 440 to 625F. specific examples in an actual: well drilling operation, Under the g Emulsi-fyiflg the P611114 but I have found that the load-carrying capacities of mate employed was an oil concentrate containing about: drilling muds,- as determined by the Timken machine, 60 percent by weightof the sodium salts of mahogany are a measure of the prolongation of bit life and other acids, said sodium salts having an average molecular advantages obtained through the use of my drilling muds Weight 0f from about 445 to The "CalciumPelfW? inactual drilling operations in the field. Since the loadna-te was an oil concentrate containing 41 percent by carrying capacities of drilling muds as obtained by the Weight of the al m salts of mahogany acids having 3 Timken machine correlate well with actualfield tests, m l u Weight of The M fi Petmnate? itis thus possible to te t th efi'icacy f drillingmud-s i was an oil concentrate containing 47 percent by weight of the laboratory to determine their suitability for use in ag s um Salts of g ny acids g molethe field. cular weight of 854. The mahogany acids employed It is characteristic of the drilling muds of this invenwere a 46 percent by weight concentrate in a lubricating tion th t they h load-carrying i i as measured oil fraction of the preferentially oil-soluble petroleum 'by the Timken machine, of not less than pounds, sulfonic acids obtained as a by-product in the refining as compared to load-carrying capacities of 15 pounds of lubricatingoil fractions with oleum. and below for conventional oil-in-water emulsion drilling n p fi ad o bcn onite, he clay p y j mu-ds which have substantially no lubricating properties. was a calcium base-exchanged bentonite in a concentra There are set forth in the following table illustrative 30 tion-of' 6 percent by weight of its suspension in water. Inexamples of drilling muds made in accordance with the preparing the calcium base-exchanged bentonite, a2 perinvention; The table also includes for purposes of comcent by Weight suspension of bentonite in water was parison a mud (Example 18) which represents the contreated with lime in the proportion of 3- poundsper ventional oil-in-water. emulsion muds of the prior art. barrel, well agitated and aged overnight. Thereafter, an All of the muds of the examples were prepared by the additional amount of dry bentonite was added, sufficient following general procedure. The oil, the asphaltic' mato give a total bentoni'te concentration in the suspension terial and emulsifying agent were mixed, and the mixture of 6 percent by weight. With the addition of the dry was heated to 180 F. and stirred for 15 minutes to obtain b'entoni-te, there occurred a slight increase in viscosity a uniform blend of the various constituents. The oily of the mud. The mud was thinned by the addition of mixture was then added to a suspension of 6 percent by 40 calcium lignosulfonate in the proportion of V2 pound weight of bentonite in water, and the entire mixture per barrel.

Sulfur-Containing Asphalt Oil Emulsifying Agent Tlmken Percent Total Oil Load- Example Percent by Wt. Phase, Carrying Type by Wt of Sulfur Type Percent Type LbJBbl. Capacity of Oil in Oil by Vol. of oi Mud (Pounds) Phase Phase Drilling Mud 1 Granular Petroleum Asphalt 30 1.0 N% htilenicExtract 10 Petronate 4 35 2 .d0 1.7 'o-l-- 4 so 3. Manjakr 20 1. 8 3 Kuwait Reduced Crude 73 3. 8 1 75 71 3.8 2 as 315 3 s5 68 3.5 3 .15 61 3.2 s 90. 46 2.4' 3 60 9.1 0.5 3 10 71 3.8 10 2. 100 71 3.8 1D Sorbitan Trloleate 2 68 3. 5 l0 stgillum Soaps of Tall 3 100 l 66 3.4 10 Calcium Pet ronate. 4 Z3 3.8 10 Magnesium Petronate- 1 68 3.5 10 Mahogany Acids" 3 100 68 3.5 a 10 do 3 100 0 0 10 Petronate 3 5 was heated in an open vessel at 140 F. with sutficien-t tirring to insure complete emulsifica-tion. Prior to test ingin the Timken machine, the oil-in-water emulsion muds thusprepared were placed in a sealed container and aged overnight. 7

Under "the Asphalt column in the table, there are shown granular petroleum asphalt, manjak and Kuwait reduced crude. The granular petroleum-asphalt employed bade sulfur content of about 315; percent, a melting point of. 325 F. and penetrations of Ozat 77 F. and 2 to 3 at It will be noted from the above table that conventional.

oil-'in-water emulsion drilling muds had substantially no. lubricating properties.

taining 10 percent by volume of diesel fuel oil was. less than 5 pounds. A mud of this type is substantially iden tical with oil-in-water emulsion muds commonly employed in the field. The addition of a sulfur-containing-xr' asphaltic'material, in accordance with the invention, re-x sulted in substantial increases in load-carrying capacity,

F., both penetrations being measured under loads of 75 ranging from the 35. pound figure shown-in Example 1 This is shown in Example 18,, wherein the load-carrying capacity of a drilling mud con tomore than 100 pounds shown in the other examples.

Examples 6 and 7, taken together, show the effect of alkali metal hydroxides on the drilling muds of the invention. The asterisk adjacent the value of load-carrying capacity shown in Example 7 indicates that this mud has been treated with alkali metal hydroxide. Example 6 is a mud of the invention Without having been treated with caustic soda and has a load-carrying capacity of 85 pounds. As shown in Example 7, when the mud of Example 6 was treated with 1 pound per barrel each of caustic soda and quebracho, the load-carrying capacity was reduced to 15 pounds, a value indicating no significant lubricating properties. It is to be noted that although quebracho was used in this test to simulate the conventional caustic soda-quebracho treatment in the field, the use of quebracho alone without caustic soda will not result in a reduction of the load-carrying capacities of the muds of the invention.

It is significant to note in the above table that, in every instance where there is set forth a composition in accordance with the invention, the load-carrying capacity is always at least 35 pounds. This indicates that the muds of my invention have desirable lubricating properties. The examples also show the variation in the amount of asphalt with its sulfur content. When employing manjak, a high sulfur content asphalt, smaller amounts of asphalt, say from 10 to 20 percent by weight of the oil phase, are utilized. When employing the Kuwait reduced crude containing smaller amounts of sulfur, larger amounts of asphalt are utilized, say fromabout 40 to 75 percent by weight of the oil phase. Example 10 shows that when using insufiicient asphalt to provide at least about one percent of sulfur in the oil phase, the resulting drilling mud has no significant lubricating properties.

It is obvious. from the foregoing detailed description of the invention that I have provided superior oil-in-water emulsion drilling muds of improved lubricating properites, which prolong the useful life of drill bits by substantially retarding failure of the bearing thereof. 'It is therefore now possible to reduce the number of rolmd trips required for replacing drill bits, to reduce the time lost in making bit changes, and-thereby to achieve substantial economies in well drilling operations. Furthermore, since fewer bits are required to drill a well, there will be less wear and tear on the drilling rig, and a relatively small, but nevertheless significant savings in the cost of bits. Also, more time will be made available to the. drilling crew for performing other essential tasks.v When employing the drilling muds of my invention, the limting factor of bit life is not the bearings, as in the past, but

the cutting teeth of the bit. The use of the drilling muds of the invention therefore confers the additional advantage of imparting a safety factor in drilling operations because a bearing failure may not be expected until after the teeth of the bit have been substantially worn out. Since bit changes will be accomplished because of tooth Wear prior to the bearings approaching a dangerous condition of wear, the likelihood of conefishing jogs is substantially reduced.

It is a further important advantage of the oil-in-water emulsion drilling muds of this invention that the oil phase thereof is capable of preferentially wetting metal surfaces. This ability of the oil phase preferentially to wet metals results in the formation of a continuous film of oil phase on the surfaces of the drill bit and the bearings thereof to the virtual exclusion of water. Accordingly, only relatively small amounts of oil phase, such as are customarily used in oilin-water emulsion drilling muds, are necessary to obtain the desired lubrication of the bearings of a drill bit in accordance with the invention. When it is considered that the main lubricating function desired of the drilling mud is directed to the small area of metal surface which constitutes the bearings of a drill bit, it will be appreciated that substantial economiesare achieved by using-the oilin-water:

emulsion muds of the invention, particularly since the additives conferring the desired lubricating properties need be based only on the oil phase and not on thefur, as set forth herein, other materials which have acontributory effect on the lubricating properties of the resulting muds. For example, as described and claimed in my copending application Serial No. 465,417, filed on even date herewith, water-insoluble, oil-soluble sulfurized organic compounds are effective in conferring improved lubricating properties on oil-in-water emulsion drilling muds. copending application Serial No. 465,419, filed on even date herewith, certain water-insoluble, preferentially oilwettable inorganic sulfides are effective in conferring lubricating properties on oil-inwater emulsion drilling muds. 1

I can add to or substitute for part of the asphaltic materials havingchemically combined sulfur of the present invention the sulfurized organic compounds or the inorganic sulfides 'of the above copending applications, or mixtures of these materials, as may be dictated by considerations'of cost and availability.

Resort may be had to such other modifications and variations as fall within the spirit of the invention and the scope of the appended claims.

I claim: I

1. A drilling mud of enhanced lubricating properties comprising an oil-in-water emulsion containing clay solids, an asphalt in the oil phase, said asphalt having chemically combined sulfur and being present in an amount sufi'icient to provide at least about one percent of sulfur by weight of the oil phase, said mud containing no amount of alkali metal hydroxide sufiicient to destroy the enhanced lubricating properties of the mud.

2. The drilling mud of claim 1, wherein said asphalt has'a's'ulfur content of at least about 1.5 percent and is present in an amount not greater than 75 percent by weight of the oil phase.

3. The drilling mud of claim 2, wherein said asphalt is an asphaltite.

4. The drilling mud of claim 2, wherein said asphalt is a natural asp halt. V V

"5. The drilling mud of claim 2, wherein said asphalt is an asphalt-containing petroleum residue.

:6. The drilling mud of claim 2, wherein said asphalt is a reduced crude and is cut back with a gas oil in pro portions of reduced crude to gas oil ranging from 1:1 to 3:1.

7. The drilling mud of claim 3, wherein the oil phase of said mud is a residual fuel oil and said asphalt is agent selected from the group consisting of preferentially oil-soluble alkylaryl sulfonic acids and metal salts thereof, the sodium soaps of tall oil, and the higher fatty acid esters of the anhydroalkitols, the amount of emulsifying agent being suificient to reduce the surface tension of the filtrate substantially below that of water, said mud containing no amount of alkali metal hydrox- Also, as described and claimed in mya 1-1 ide siifiie'ient t'd destrdy the e hanced lubricating prb er alsb'eon'taining an asphalt in the oil phase having at" least about 115 percent by weight of chemically combined sulfur, s'aid asphalt being present in an amount sufficient to provide at least about one percent of sulfur by weight of the'oil phase, sa'id mud containing no amount} of alk ali metal hydroxide sufiicient to destroy the enhanced lubricating propertie'sflof the mud.

l4; The drilling mud-of claim 13, wherein the asphalt isa reduced crude and is employed: in an amount of fr dm aljout' 40 to 75 percent by weight of the oil phase.

' 15. The drilling mud of claim' 13, wherein there is resen'ean emulsifying agent selected from the group consisting of preferentially oil-soluble alkylaryl sulfonic acids and metal salts thereof, the sodium soaps of tall oil; and the" higher fatty acid esters of the anhydroalkitors; the amount of emulsifying agent being sufficient to reduce' 'tiie" surface tension of the filtrate substantially below that of Water.

'16-. A- drilling mud of enhanced lubricating properties comprising an oil-in-Water emulsion containing clay snlids and-from about 1 to 4 pounds per barrel of mud of an emulsifying agent selected from the group consisting of preferentially oil-soluble alkylaryl sulfonic acids and metal salts thereof, the sodium soaps of tall oil, and the higher" fatty acid esters of the anhydroalkitols, the oil phase'of said emulsion constituting from 5 to 25 pefc'e nt by Volume of said drilling mud and comprising a} uniform blend of from'about 40 to 75 percent of a sulruaeontaining reduced crude oilby weight and a petfdleurii distillate fraction, the sulfur content of said 1'e'- du'cd' crude being suflicient to provide at least about one percent of' sulfur by Weight of the oil phase, said niud containing no amount of alkali metal hydroxide sufficient to destroy the enhanced lubricating properties of the mud. t

17. The drilling mud of claim 16,- Wherein the reduced erude'is a Kuwait reduced crude from the Burgan field and has a sulfur content content of about 5 percent.

18. A uniform blend of oily material's, useful in the mud, which comprises adding t'o'said water-base'dr u'lliii'g mud in the drilling'fl'uid system of said well, a'n--oil, an emulsifying agent,'- and an asphalt having chemically'i combined sulfur in amounts effective to convert said water-base drilling mud to an oil-in-water' ern'ulsinn drilling mudcontaining at least about one percent of",

sulfur by weight of the oil phase, said mud containing no amount of alkali metal hydroxide sufiicient to destroy the enhanced lubricating properties of then'aud, circulat tem, and continuing drilling of the Welli 20. The process of claim 19, wherein-the emulsifying: agentis selected front the group consisting of pref'rentially' oil-soluble alkylaryl sulfonie acids and metal salts thereof, the sodium soaps of talloil, and thehigher fat ty acid esters of'theanhydroalkitols.

21. A process of drilling a well with a I'otarY 'bitWhicli ing the' resulting mixture through said drillingrr'ilid-syscomprises'form'ing aborehole with said bitwhile' circulat ing a drilling mud of enhanced lubricatingprope'rties through said borehole, said drilling mudcomprising 1i oil-in-water emulsion containing clay solids; an asphalt in the" oil phase, said asphalt having'chemieally' cbni bined sulfur and being present in an amount siifiieieftt to provide at least about one percent of sulfur by Weight of the oil phase, said mud containing no amountof allfali" metal hydroxide sufficientto destroy the-enhancedrluhrieating properties ofthe mud.'

References Cited in the file of this pa'ten't' UNITED-STATES PATENTS 2,423,144 Gregg Ju1y 1-, 1 947 2,689,219 Menaul Sept. 14,1 1954 FOREIGN PATENTS 476,310 Canada Aug: 21, i

OTHER REFERENCES Davey: The Mechanism of Action of Extreme Pres sure" Lubricants, article in Scientific Lubrication, Sept." 1949, pages 7, 8, 11 and 14. I

Rogers: Composition and-Properties of Oil Well Diill ing Fluids, Revised Edition, p'ub. 1953 by Gulf Pub: of Houston, Texas, pa'gesSll, 513, and 514; 

1. A DRILLING MUD OF ENHANCED LUBRICATING PROPERTIES COMPRISING AN OIL-IN-WATER EMULSION CONTAINING CLAY SOLIDS, AN ASPHALT IN THE OIL PHASE, SAID ASPHALT HAVING CHEMICALLY COMBINED SULFUR AND BEING PRESENT IN AN AMOUNT SUFFICIENT TO PROVIDE AT LEAST ABOUT ONE PERCENT OF SULFUR BY WEIGHT OF THE OIL PHASE, SAID MUD CONTAINING NO AMOUNT OF ALKALI METAL HYDROXIDE SUFFICIENT TO DESTROY THE ENHANCED LUBRICATING PROPERTIES OF THE MUD. 